Technology using liquid crystals for displays is increasingly common in today's electronic applications. Liquid Crystal Display (LCD) and Liquid Crystal on Silicon (LCOS) are examples of such technology.
In many liquid crystal applications, a display needs to be illuminated instantaneously and for short periods of time. Liquid crystal pixels, however, are characterized by a response time representative of the time required for pixels to transition from being completely dark to a certain brightness level. Accordingly, pixels may not be provided sufficient time to reach desired brightness levels when the display is turned on for periods shorter than the response time of the pixels.
This problem becomes more severe in the case of a line-addressed display, where the display is illuminated sequentially one row at a time. What typically happens is known as a “brightness gradient” effect; rows of the display that are illuminated first (typically the upper rows of the display) receive more time to transition to their desired brightness levels than their subsequent counterparts. Accordingly, the perceived brightness of the display is vertically non-uniform.
A first solution to the above problem attempts to equalize brightness across the display by deliberately darkening certain sections of the display. Brightness equalization techniques, however, negatively affect the contrast ratio of the display defined as the ratio of maximum to minimum brightness of the display.
A second solution to the above problem uses direct addressing to illuminate the display. Direct addressing allows for each pixel of the display to be illuminated independently. Accordingly, it is possible, using direct addressing, to simultaneously illuminate every pixel of the display. While direct addressing seems to solve the “brightness gradient” problem, it is not a viable solution for large displays having thousands of pixels. This is because direct addressing requires separate addressing circuitry and a voltage loading buffer for each pixel of the display.
What is needed therefore are methods and systems that offer scalable solutions for display illumination that do not suffer from the problems described above.